JP2014526638A - Reciprocating positive displacement pump with reversing motor - Google Patents

Abstract

The pump system includes an electric motor, a pump, a conversion device, and a controller. The electric motor has an output shaft that is rotatable in a first rotation direction and a second rotation direction opposite to the first rotation direction. The pump has an input shaft that is linearly movable in a first linear direction and a second linear direction opposite to the first linear direction. The conversion device connects the output shaft to the input shaft, converts the rotational motion of the output shaft in the first rotational direction to the movement of the input shaft in the first linear direction, and converts the output shaft in the second rotational direction. The rotational motion is converted into a movement of the input shaft in the second linear direction. The controller repeatedly reverses the rotation of the output shaft to generate a reciprocating motion of the input shaft.
[Selection] Figure 1

Description

  The present invention relates to a positive displacement pump system, and more particularly to a reciprocating pump drive system and a reciprocating control method.

  Positive displacement pumps have a mechanism that draws a volume of material into an expanding chamber and pushes the material out of the chamber when contracted. Such a pump generally includes a reciprocating pump mechanism such as a piston or a rotary pump mechanism such as a combination of a set of gears. The reciprocating piston pump requires two-way input that can drive the piston to expand and contract the pump chamber. A typical pump mechanism is driven by a rotational input such as a motor having a rotational output shaft. Conventionally, such a motor is composed of an air motor that operates with compressed air or an electric motor that operates with an alternating current. Therefore, in the case of rotational input, it is necessary to convert rotation in a single direction of the output shaft into reciprocating motion. Such a conversion is performed by a crankshaft or cam mechanism such as that disclosed in US Pat. No. 5,637,097, issued to Lehrke et al. And assigned to Graco Inc.

US Pat. No. 5,145,339

  In the air motor, the compressor must be driven by the motor, and the compressed air is converted into a rotational motion, and further, the rotational motion is converted into a reciprocating motion. Therefore, the efficiency is low in terms of energy consumption. In addition, air motors and compressors that drive air motors generate an undesirable amount of noise, which can lead to problems associated with icing due to air compression and expansion. Electric motors achieve energy efficiency over air motors, but still require a complex mechanism to convert unidirectional rotational motion into two-way linear reciprocating motion for the pump. Accordingly, there is a need for an improved drive mechanism for a reciprocating positive displacement pump.

  The pump system includes an electric motor, a pump, a conversion device, and a controller. The electric motor has an output shaft that can rotate in a first rotation direction and a second rotation direction opposite to the first rotation direction. The pump has an input shaft that can move in a first linear direction and a second linear direction opposite to the first linear direction. The conversion device connects the output shaft to the input shaft, converts the rotational motion of the output shaft in the first rotational direction into linear motion of the input shaft in the first linear direction, and outputs the output shaft in the second rotational direction. Is converted into a linear motion of the input shaft in the second linear direction. The controller repeatedly reverses the rotation of the output shaft to generate a reciprocating motion of the input shaft.

  The operation method of the pump is to repeatedly reverse the direction of the current flowing through the electric motor to alternately switch the rotation of the output shaft of the electric motor between clockwise and counterclockwise, and clockwise and counterclockwise of the output shaft. A step of converting the rotational motion alternating with the rotation into a linear reciprocating motion of the pump shaft.

It is a schematic block diagram of a pump system having a positive displacement pump driven by a two-way rotation type electric motor via a motion converter. FIG. 2 is a perspective view of a pump system having the configuration of FIG. 1 in which a linear reciprocating piston pump is driven by a brushless DC motor. FIG. 3 is an exploded view of the pump system of FIG. 2 showing a reduction gear mechanism that connects the output shaft of a brushless DC motor to the input shaft of a linear reciprocating piston pump. FIG. 4 is a perspective view of the pump system of FIG. 3 showing an output shaft pinion gear and an input shaft rack gear connected by a reduction gear mechanism. It is a graph which shows direction of the electric current input into the brushless DC motor of FIGS. 2-4 with progress of time. It is a graph which shows the stroke of the pump shaft of the linear reciprocating piston type pump of FIGS. 2-4 with progress of time.

  FIG. 1 is a schematic configuration diagram of a pump system 10 having a positive displacement pump 12 driven by an electric motor 14 and a motion conversion device 16. The pump 12 draws fluid such as paint from the reservoir 18 and supplies pressurized fluid to the spray 20. Fluid that has not been consumed by the spray 20 is returned to the reservoir 18. The drive shaft 22 of the electric motor 14 and the pump shaft 24 of the pump 12 are mechanically connected to the motion conversion device 16. The motion conversion device 16 generates a reciprocating motion of the pump shaft 24 from the rotational motion of the drive shaft 22. The discharge port 26 of the pump 12 is connected to the reservoir 18 via the flow path 30A, and the inlet 28 of the pump 12 is connected to the reservoir 18 via the flow path 30B. The spray 20 is connected to the flow path 30 </ b> A by a hose 32. The electric motor 32 is electrically controlled by a controller 34, and the controller 32 includes a position sensor 35.

  The electric motor 14 supplies power to the drive shaft 22 when electric power is supplied from the controller 34. In the illustrated embodiment, the electric motor 14 is a rotary motor in which the drive shaft 22 rotates around the central axis. The controller 34 is electrically connected to the electric motor 14 and controls the rotation of the drive shaft 22 by controlling the current supplied to the electric motor 14. In the embodiment described later based on FIGS. 2 to 4, the electric motor 14 is a brushless direct current (DC) motor. However, the electric motor 14 may be a brushed DC motor or a permanent magnet AC (AC) motor.

  The rotation of the drive shaft 22 rotates the conversion mechanism in the motion conversion device 16. The motion conversion device 16 converts the rotational motion of the drive shaft 22 into linear motion of the pump shaft 24. Specifically, the motion conversion device 16 converts the rotational motion in one direction of the drive shaft 22 into movement in one direction of the pump shaft 24. In the embodiment described later with reference to FIGS. 2 to 4, the motion conversion device 16 includes a rack and pinion mechanism, and the drive shaft 22 rotates a pinion gear that meshes with a linear rack gear connected to the pump shaft 24. In general, the motion conversion device 16 includes a reduction gear mechanism. For example, the reduction gear mechanism reduces the speed of the pump shaft 24 compared to the drive shaft 22. However, the motion conversion device 16 may be composed of another type of conversion mechanism such as a cam mechanism or a crank mechanism.

  The motion conversion device 16 is connected to the pump shaft 24 of the pump 12. The pump 12 is a positive displacement pump that expands and contracts the pump chamber by the reciprocating motion of the pump shaft 24. In an embodiment to be described later with reference to FIGS. 2 to 4, the pump 12 is a linear reciprocating piston type in which a piston is provided in a cylinder, draws fluid from the inlet 28, and pushes pressurized fluid from the outlet. It consists of a pump. However, the pump 12 may be another type of positive displacement pump such as a diaphragm pump.

  The pressurized fluid is discharged from the discharge port 26 and fed to the reservoir 18 through the flow path 30A. The pump 12 draws the fluid before pressurization from the reservoir 18 through the flow path 30 </ b> B and the inlet 28 by the pump mechanism of the pump 12. The spray 20 is connected in parallel with the reservoir 18 and draws pressurized fluid from the flow path 30A. The spray 20 is selectively operated to discharge the fluid in the reservoir 18. The spray 20 may be manually operated directly or may be operated by a controller as part of an automated spray process.

  In the present invention, the pump system 10 uses a reversible electric motor such as a brushless DC motor 14 and is a linear actuator such as a motion converter 16 for reciprocating a pump such as a piston type pump 12. Give power. In an embodiment using a brushless DC motor, the controller 34 is operative to supply a reversing current to the brushless DC motor 14 to generate a reciprocating motion. More specifically, the controller 34 switches the rotation direction of the drive shaft 22 by reversing the direction of the current flowing through the brushless DC motor 14. Brushless DC motors have low inertia and can quickly reverse the direction of rotation in response to a change in current direction. Moreover, since the brushless DC motor can obtain the maximum torque even when the rotational speed is zero, the pump 12 can maintain the maximum pressure, which is similar to the response performance of the fluid motor. In addition, it can be obtained without causing noise, cost, and icing problems. In a brushless DC motor, there is a direct relationship between the supplied current and the shaft torque. Accordingly, only the speed of the electric motor 14 can be changed while maintaining the discharge pressure of the pump 12 constant by the constant output torque (and current) of the electric motor 14. Furthermore, as another feature of the present invention, the controller 34 uses the position sensor 35 to monitor the position of the pump shaft 24, thereby causing the pump 12 to reverse and change irregularly. It is possible to suppress wear of the internal components.

  FIG. 2 is a perspective view of the pump system configured as shown in FIG. 1 in which the linear reciprocating piston pump 12 is driven by the brushless DC motor 14. The linear reciprocating piston pump 12 and the brushless DC motor 14 are accommodated in a housing 36, and the motion conversion device 16 (not shown in FIG. 2) is also accommodated in the housing 36. The motion conversion device 16 includes a reduction gear mechanism 38 mounted in the housing 36. The reduction gear mechanism 38 has a shaft 40 and a shaft 42, and connects the pinion gear on the brushless DC motor 14 side to the rack gear on the linear reciprocating piston pump 12 side. The linear reciprocating piston pump 12 includes an inlet 28, a discharge port 26, a cylinder 44, and a shaft cover 46. The shaft cover 46 accommodates an input shaft (FIG. 3) for the linear reciprocating piston pump 12. ing. The linear reciprocating piston pump 12 is assembled to the housing 36 via a tie rod 50A (FIG. 3), a tie rod 50B (FIG. 3), and a tie rod 50C (FIG. 3). The tie rod 50A, the tie rod 50B, and the tie rod 50C are linear reciprocating piston types so that the pump shaft 24 in the shaft cover 46 can be driven by the brushless DC motor 14 via the motion conversion device 16 and the reduction gear mechanism 38. The pump 12 is held fixed to the housing 36.

  FIG. 3 is an exploded view of the pump system 10 of FIG. 2 showing a reduction gear mechanism 38 that couples the drive shaft 22 of the brushless DC motor 14 to the pump shaft 24 of the linear reciprocating piston pump 12. The motion conversion device 16 (FIG. 1) includes a reduction gear mechanism 38, and the reduction gear mechanism 38 includes a first gear mechanism 56 and a second gear mechanism 58. The housing 36 includes a housing main body 36A, a gear cover 36B, and a motor cover 36C.

  The brushless DC motor 14 is inserted into a cavity in the housing main body 36A so that the drive shaft 22 extends through the opening 60A and serves as an output shaft that drives the reduction gear mechanism 38. The motor cover 36 </ b> C is disposed to face the housing main body 36 </ b> A and accommodates the brushless DC motor 14. The shaft 40 of the first gear mechanism 56 is held between the opening 60B of the housing main body 36A and the opening 60C of the gear cover 36B. The shaft 42 of the second gear mechanism 58 is held in the opening 60D of the gear cover 36B and extends into the cavity 62 of the housing body 36A. The pump shaft 24 serves as an input shaft for operating the linear reciprocating piston pump 12. One end of the pump shaft 24 of the linear reciprocating piston pump 12 extends into the cavity 62 of the housing main body 36A, and is connected to the second gear mechanism 58 via a rack gear (see the rack gear shown in FIG. 4). . The other end of the pump shaft 24 extends into the cylinder 44 through the shaft cover 46 and drives a piston (not shown). The tie rod 50A, the tie rod 50B, and the tie rod 50C connect the base 64 of the linear reciprocating piston pump 12 to the base 66 of the housing main body 36A. The cover member 46A and the cover member 46B are disposed so as to surround the pump shaft 24 inside the tie rod 50A, the tie rod 50B, and the tie rod 50C. The inlet 28 of the linear reciprocating piston pump 12 is connected to a fluid supply source before pressurization, such as a flow path 30B (FIG. 1). The discharge port 26 of the linear reciprocating piston pump 12 is connected to a fluid supply device such as a spray 20 (FIG. 1).

  In one embodiment, the brushless DC motor 14 is mounted in the housing 36 such that the drive shaft 22 faces in a direction orthogonal to the pump shaft 24. For example, operation of the pump system 10 on a flat surface such as a floor is contemplated. The pump shaft 24 is configured to be substantially perpendicular to the flat surface. Therefore, the electric motor 14 is generally attached in a direction perpendicular to the pump shaft 24 and parallel to the flat surface. For this reason, the rotation of the drive shaft 22 can be easily converted into a linear motion in the vertical direction of the pump shaft 24 by using a rack and pinion mechanism or the like. The brushless DC motor 14 rotates the drive shaft 22 and applies rotation to the first gear mechanism 56. The first gear mechanism 56 rotates the second gear mechanism 58, and the second gear mechanism 58 moves the pump shaft 24 of the linear reciprocating piston pump 12 via a rack gear (not shown). The pump shaft 24 drives a piston in the cylinder 44, the fluid before pressurization is drawn from the inlet 28, and the pressurized fluid is discharged from the discharge port 26. In one embodiment of the present invention, the linear reciprocating piston pump 12 comprises a four ball piston pump such as can be purchased from Graco Inc. An example of a four ball piston pump is generally described in US Pat. No. 5,368,424, assigned to Powers and assigned to Graco Inc. The cover member 46 </ b> A and the cover member 46 </ b> B particularly prevent dust, dust, and dust from entering the cylinder 44 through the opening for the pump shaft 24. The tie rod 50A, tie rod 50B, and tie rod 50C housing the linear reciprocating piston pump 12 so that the motion conversion device 16 including the reduction gear mechanism 38 can reciprocate the pump shaft 24 with respect to the cylinder 44. Hold firmly apart from 36. Accordingly, the tie rod 50A, the tie rod 50B, and the tie rod 50C oppose the force generated by the brushless DC motor 14 and applied to the linear reciprocating piston pump 12.

  In the assembled state, the reduction gear mechanism 38 forms a power transmission coupling between the pinion gear 68 of the drive shaft 22 and the rack gear 70 (FIG. 4) of the pump shaft 24. That is, the pinion gear 68 meshes with the input gear 56 </ b> A of the first gear mechanism 56. The output gear 56B meshes with the input gear 58A of the second gear mechanism 58, and this input gear 58A drives the output gear 58B. The output gear 58B provides rotational input to the rack gear 70. In this manner, the linear movement of the pump shaft 24 occurs due to the rotation of the drive shaft 22 by the brushless DC motor 14. The motion conversion device 16 including the reduction gear mechanism 38 has a unidirectional force from the drive shaft 22 to the pump shaft 24 such that a single direction movement of the pump shaft 24 corresponds to a single direction rotation of the drive shaft 22. Only communicate. The direction of rotation of the drive shaft 22 by the brushless DC motor 14 is reversed by the controller 34 (FIG. 1), and the pump shaft 24 is repeatedly reciprocated to obtain the pump operation of the piston in the cylinder 44.

  4 is a perspective view of the pump system 10 of FIG. 3 showing the pinion gear 68 of the drive shaft 22 (FIG. 3) and the rack gear 70 of the pump shaft 24 connected by the reduction gear mechanism 38. As shown in FIG. The housing 36 is not shown in FIG. 4 so that the assembly of the components of the pump system 10 can be seen. The rotation of the drive shaft 22 by the brushless DC motor 14 causes a linear movement of the pump shaft 24 of the linear reciprocating piston pump 12. The brushless DC motor 14 is supplied with a DC current whose direction of flow is reversed from the controller 34 (FIG. 1), and rotation of the drive shaft 22 occurs in two alternate directions, that is, in two alternate directions.

  In the first period, a DC current flowing in the first direction is supplied to the brushless DC motor 14 to cause the clockwise drive shaft 22 to rotate, and as a result, the pump shaft 24 of the linear reciprocating piston pump 12. Is moved upward in FIG. The clockwise rotation of the pinion gear 68 causes the input gear 56A to rotate counterclockwise. Since the input gear 56A has a larger diameter than the pinion gear 68, the input gear 56A rotates at a lower speed than the pinion gear 68. The input gear 56A and the output gear 56B are attached to the shaft 40, and the output gear 56B rotates counterclockwise at the same rotational speed as the input gear 56A. The output gear 56B meshes with the input gear 58A of the second gear mechanism 58, and the input gear 58A rotates clockwise due to the counterclockwise rotation of the output gear 56B. The input gear 58A has a larger diameter than the output gear 56B, and rotates at a lower speed than the output gear 56B. The input gear 58A and the output gear 58B are attached to the shaft 42, and the output gear 58B rotates clockwise at the same rotational speed as the input gear 58A. In this way, the clockwise rotation of the output gear 58B is decelerated compared to the clockwise rotation of the pinion gear 68. The specific degree of deceleration is set according to the individual characteristic values of the brushless DC motor 14 and the linear reciprocating piston pump 12 and the required output of the pump system 10. As the output gear 58B rotates clockwise, the rack gear 70 is pushed upward in FIG.

  The pump shaft 24 is also pushed upward by the upward movement of the rack gear 70. The distance that the pump shaft 24 moves upward is directly related to the period during which the controller 34 rotates the drive shaft 22 in the first direction. Therefore, the stroke length of the pump shaft 24, that is, the stroke length of the piston in the cylinder 44 directly corresponds to the period during which a current flowing in a predetermined direction is supplied to the brushless DC motor 14. As the pump shaft 24 moves away from the linear reciprocating piston pump 12, fluid is drawn from the inlet 28.

  In order to return the pump shaft 24 back into the cylinder 44 and push out the fluid pressurized by the cylinder 44 from the discharge port 26, the controller 34 rotates the drive shaft 22 in the second direction opposite to the first direction. Is reversed. In one embodiment, the controller 34 reverses the direction of current flowing through the brushless DC motor 14. Such reversal can be performed by reversing the polarity of the current in the armature of the brushless DC motor 14 as already known. As a result, the rack gear 70 is pushed downward (in FIG. 4) through the action of the first gear mechanism 56 and the second gear mechanism 58, and the pump shaft 24 is pushed into the cylinder 44. In this manner, the controller 34 (FIG. 1) causes the pump shaft 24 to linearly reciprocate by repeatedly reversing the direction of the current continuously flowing to the brushless DC motor 14 over a period of time.

  The control parameter of the brushless DC motor 14 is set by the operator of the pump system 10 based on the required output of the linear reciprocating piston pump 12. For this reason, the controller 34 is composed of a computer system having a processor, a memory, a graphic display, a user interface, and the like as is well known. The controller 34 commands the magnitude of the current supplied to the brushless DC motor 14, the reversal of the polarity (direction) of the current, and the period for each polarity of the current supplied to the brushless DC motor 14. The controller 34 operates to keep the magnitude of the current supplied to the brushless DC motor 14 at each polarity constant. A constant output torque is obtained from the brushless DC motor 14 by a constant current. Torque from the drive shaft 22 is immediately transmitted to the pump shaft 24 by the pinion gear 68, the reduction gear mechanism 38, and the rack gear 70 with a linear relationship. Therefore, the rotational speed of the drive shaft 22 is affected by the reaction force acting on the drive shaft 22 via the reduction gear mechanism 38 due to the pressure in the linear reciprocating piston pump 12. As described above, since the brushless DC motor responds quickly to changes in the input current, the brushless DC motor 14 can quickly reverse the direction of rotation and maintain the output torque in a unidirectional manner while maintaining the output torque at the end. The rotation is actually stopped for a moment between the rotation and the rotation in the other direction (at this time, the rotation speed is equal to 0). Therefore, the controller 34 operates the brushless DC motor to reciprocate the pump shaft 24 without requiring a complicated mechanical device for converting the rotational motion of the output shaft into reciprocating motion of the pump shaft in two directions. Can be made. In addition, the brushless DC motor is quieter and uses less power than the conventional air motor. As described above, the pump system 10 can reduce noise and improve the operation cost as compared with other systems.

  FIG. 5A is a graph showing the input current (i) to the brushless DC motor 14 shown in FIGS. 2 to 4 together with the passage of time (t). FIG. 5B is a graph showing the stroke (d) of the pump shaft 24 of the linear reciprocating piston pump 12 shown in FIGS. 2 to 4 with the passage of time (t). According to FIG. 5A, the magnitude of the current i is substantially the same at all time points. Accordingly, the output torque of the drive shaft 22 is substantially constant. For example, at the time point A, the controller 34 operates to supply a current flowing in the positive direction to the brushless DC motor 14, and the pump mechanism 24 is moved upward by the action of the gear mechanism. Next, the controller 34 operates to immediately supply a current flowing in the negative direction to the brushless DC motor 14 with the same magnitude as the current in the positive direction. Such inversion causes the pump shaft 24 to move downward. Therefore, a complete one reversal cycle of pumping occurs between time A and time B. The direction of the current i flowing over a certain period is continuously switched alternately between the positive direction and the negative direction over a desired period, and the pump shaft 24 continues to reciprocate.

  One reversal cycle of pump operation consisting of an upward movement stroke and a downward movement stroke of the pump shaft 24 is completed by a pair of positive current and negative current. The length of the period in which each reversal cycle of pump operation occurs may be changed to improve the performance of the pump system 10 as will be described later. In the present embodiment, each of the positive period and the negative period increases over the illustrated period. Therefore, the second pump reversal interval that occurs between time B and time C is longer than the first pump reversal interval that occurs between time A and time B. Each subsequent pump reversal interval gradually increases with time. As a result, the pump shaft 24 reciprocates over a longer linear distance, and the stroke length of the piston in the cylinder 44 increases as shown in FIG. 5B. Due to such a change in the stroke length of the pump shaft 24, the direction of the pump shaft 24 is reversed when the gear meshing positions in the reduction gear mechanism 38, the pinion gear 68, and the rack gear 70 are different, thereby causing wear in the gear mechanism. The distribution of is improved.

  As shown by a solid line in FIG. 5B, the stroke d of the piston in the piston cylinder 44 increases from time A to time D. For example, the stroke d of the piston increases toward a specific point between time A and time B, and then returns toward the starting point. At each subsequent pump reversal, the stroke d gradually increases. Thus, in the same time frame of FIG. 5B corresponding to time point A to time point B in FIG. 5A, an increase in stroke length is shown. After the stroke length has increased and all or most of the cylinder 44 has been used at time D, the stroke length may be gradually decreased. 5A and 5B, a time point that is axisymmetric about the vertical axis at the time point D from the time point A to the time point B may be determined, and the current reversal interval and the stroke length may be gradually shortened.

  Advantages of varying the stroke length include an increase in the service life of the pump system 10. That is, the service life of the gear mechanism of the motion conversion device 16 is increased. Due to the reversing operation of the pump, an impact load is applied to the gear teeth, particularly the teeth of the pinion gear 68. This is particularly noticeable when the pump inversion period is minimized and the drive shaft 22 rapidly reverses direction. By changing the stroke length of the pump shaft 24, the gear teeth meshing with each other when the reversal occurs are changed, whereby the gear teeth to which the impact load is applied are more dispersed. Furthermore, the position of the bearing in the pump system 10 is changed by changing the position where reversal occurs in the portion along the shaft support region in the pump system 10 such as the portions along the pump shaft 24, the shaft 40, and the shaft 42. The service life of is increased.

  The solid lines in FIGS. 5A and 5B indicate a linear and uniform change in stroke length in a predetermined pattern. As shown in FIG. 5A, a complete reversal cycle of pumping occurs between time A and time B. Each inversion period is equally allocated to a positive current and a negative current. Due to such an even distribution, there is not enough room to achieve a predetermined pump stroke, so that the pump shaft 24 projects the piston in the cylinder 44 from the end of the cylinder 44 or collides with the end. Will definitely disappear. However, the stroke length may be changed irregularly or may be changed unevenly. As long as the controller 34 monitors the absolute position of the piston or a setting pattern is provided to prevent the piston in the cylinder from protruding, the time distribution between the positive current and the negative current in each pump reversal period is changed. It is possible. For this purpose, the controller 34 uses the position sensor 35 to monitor the absolute position of the pump shaft 24 relative to the cylinder 44. Instead, a position sensor may be provided in the cylinder 44 to monitor the position of the piston.

  For example, the solid line in FIG. 5B indicates that the position (indicated by the vertex) for switching from upward movement to downward movement can be changed, but from downward movement to upward movement. The switch to is always done at the same initial position (indicated by the valley). However, the broken line indicates that the switching from the downward movement to the upward movement may be performed at a different position. In this way, the stroke range is always maintained within the entire usable area of the cylinder 44, while the position where the reversal occurs with each stroke can be changed. Therefore, not only can the stroke length be changed, but also the position of reversal in each stroke can be changed with respect to the position of the pump shaft 24 with respect to the cylinder 44 (and the meshing position of the gear mechanism in the motion conversion device 16). is there.

  Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in detail without departing from the spirit and scope of the invention.

Claims (23)

An electric motor having an output shaft that can rotate by being reversed to a first rotation direction and a second rotation direction opposite to the first rotation direction;
A pump having an input shaft movable in a first linear direction and a second linear direction opposite to the first linear direction;
The output shaft is connected to the input shaft, the rotational movement of the output shaft in the first rotational direction is converted into the movement of the input shaft in the first linear direction, and the rotational shaft in the second rotational direction is converted. A conversion device that converts rotational movement of the output shaft into movement of the input shaft in the second linear direction;
And a controller that repeatedly reverses the rotation direction of the output shaft to generate a reciprocating motion of the input shaft.   The pump system according to claim 1, wherein the pump is a positive displacement pump.   The pump system according to claim 1, wherein the conversion device includes a rack and pinion mechanism.   The pump system according to claim 3, wherein the conversion device further includes a reduction gear mechanism.   The pump system according to claim 4, wherein the reduction gear mechanism includes a two-stage reduction mechanism. The electric motor is a brushless DC motor,
The pump system according to claim 1, wherein the controller reverses a direction in which a current supplied to the electric motor flows to reverse a rotation direction of the output shaft.   The pump system according to claim 6, wherein the controller maintains a constant output torque of the electric motor.   The pump system according to claim 6, wherein the controller changes a time interval for reversing a direction in which a current flows.   9. The pump system according to claim 8, wherein the controller changes time intervals for reversing the direction in which the current flows one after another for each time interval.   10. The pump system according to claim 9, wherein the controller changes the time interval for reversing the direction in which the current flows, and gradually increases and decreases between the upper limit and the lower limit. Repeatedly reversing the direction of the current flowing in the electric motor, and rotating the output shaft of the electric motor alternately clockwise and counterclockwise;
And a step of converting the alternating rotational movement of the output shaft clockwise and counterclockwise into a linear reciprocating motion of the pump shaft. The electric motor is a brushless DC motor,
The pump operation method according to claim 11, wherein the pump is a positive displacement pump. The step of converting alternating rotational movement of the output shaft clockwise and counterclockwise into linear reciprocation of the pump shaft,
Rotating the pinion gear on the output shaft;
The method of operating a pump according to claim 11, further comprising a step of linearly moving a rack gear with the pinion gear. The clockwise rotation of the output shaft generates a linear movement of the pump shaft in a first direction;
The pump operation according to claim 11, wherein the rotation of the output shaft in the counterclockwise direction generates a linear movement of the pump shaft in a second direction opposite to the first direction. Method. Supplying a constant current to the electric motor to maintain a constant output torque;
The method for operating a pump according to claim 11, further comprising a step of maintaining a constant pressure output from the pump.   The method of operating a pump according to claim 11, further comprising a step of changing a time interval for reversing the direction in which the current flows.   The pump operating method according to claim 16, wherein the time interval for reversing the direction in which the current flows is changed in a regular repeating pattern.   18. The method of operating a pump according to claim 17, wherein the time interval for reversing the direction of current flow is gradually increased and gradually decreased between an upper limit and a lower limit.   The pump operation method according to claim 16, wherein the time interval for reversing the direction in which the current flows is irregularly changed.   The method of operating a pump according to claim 16, further comprising a step of changing a stroke length of the pump shaft.   The pump operating method according to claim 16, further comprising a step of changing a reverse position of the pump shaft that reverses linear movement of the pump shaft. A brushless DC electric motor having a rotating output shaft;
Positive displacement pump with linearly moving input shaft;
The output shaft is connected to the input shaft, the clockwise rotation of the output shaft is converted into the movement of the input shaft in a first direction, and the counterclockwise rotation of the output shaft is converted to the first shaft. A rack-and-pinion conversion device that converts the movement of the input shaft in a second direction opposite to the direction;
A controller that repeatedly reverses the rotation direction of the output shaft to generate reciprocation of the input shaft. The rack and pinion conversion device is
A pinion gear assembled to the output shaft;
A rack gear assembled to the input shaft;
The pump system according to claim 22, further comprising: a reduction gear mechanism assembled to the pinion gear and the rack gear.